The Programmable Logic Controller (PLC) was invented in the 1960's for the automotive manufacturing industry. Since this time, virtually all successful manufacturing facilities now use them to automate the production line. PLCs are the hub of the manufacturing processes. These microprocessor-based units are used in processes as simple as conveyors to processes as complex as controlling and tracking sophisticated environment-critical manufacturing processes. They are used in virtually all new manufacturing, processing, assembly and monitoring equipment in one form or another.
The microprocessor or processor module is the “brain” of a PLC system. It consists of the microprocessor, memory integrated circuits, and circuits necessary to store and retrieve information from memory. It also includes communications ports to other peripherals, other PLC's or programming terminals. Today's processors vary widely in their capabilities to control real world devices. Some control as few as 6 inputs and outputs (I/O) and others 40,000 or more. One processor can control more than one process or manufacturing line. Processors are often linked together in order to provided continuity throughout the process.
The number of inputs and outputs PLCs can control are limited by the overall capacity of the PLC system hardware and memory capabilities. The inputs and outputs may be either discrete or analog signals. The job of the processor is to monitor status or state of input devices, scan and solve the logic of a user program, and set the appropriate state of the output devices.
For example, in an exemplary assembly line, electric torque guns are controlled by a torque controller that monitors and drives the gun to various parameters stored in the controller. Several parameter sets can be stored in the controller, and these are selected by a master control device such as a Programmable Logic Controller through discrete input signals.
One main PLC for an assembly line often communicates to several torque controllers on the line in an asynchronous manner. The number of torques and parameter sets vary for each station depending on the build process and work content. Initial plant start-up and new products introduced to the plant often cause changes in the torque sequence, number of torques, and parameter sets for the various stations. Additionally, as new products are introduced and old products phased out, entire torque stations can be added and/or removed from the production line.
All of these changes require modifications to the PLC logic that, in a conventional system, can be quite costly and often requires days or weeks to implement and validate. It would therefore be desirable to provide a system and method to allow greater flexibility in changing, adding, and/or removing PLC operation sequences in a timely manner.